The present invention relates to dispersants for use in fuels and in engine oil lubricants, especially for reducing soot-induced viscosity increase in heavy duty diesel engine lubricants.
Heavy duty diesel vehicles may use exhaust gas recirculation (EGR) engines in efforts to reduce environmental emissions. Among the consequences of recirculating the exhaust gas through the engine are different soot structures and increased viscosity of the oil at lower soot levels, compared with engines without EGR. It is desirable that oil exhibit minimal viscosity increase, e.g., less than 12 mm2/sec (cSt) at a soot loading of 6 weight % in a Mack T-11 EGR engine test.
Current methods used to disperse EGR soot include the use of dispersant viscosity modifiers (DVM's) consisting of a maleinated ethylene/propylene copolymer capped with an aromatic amine. One such aromatic amine is 4-aminodiphenylamine (ADPA) as discussed in Nalesnik, et al., U.S. Pat. No. 4,863,623.
U.S. Pat. No. 4,234,435, Meinhardt et al., Nov. 18, 1980, discloses a composition wherein a succinated polybutene is condensed with either an alkyl polyamine to make a succinimide dispersant or an alkyl polyol to make a succinic ester dispersant. U.S. Patent Application 2006/0025316, published Feb. 2, 2006, discloses a reaction product of a polymer comprising carboxylic acid functionality and an amine where the resulting product is used as a viscosity modifier in a lubricant.
The present invention provides an alternative to the DVM's discussed above for improved soot handling by using a succinic ester-containing dispersant. It is known that ester containing dispersants disperse sludge well but are not good soot dispersants. It is surprising then, that the ester-containing dispersants described herein show excellent soot dispersive characteristics.
The present invention, therefore, solves the problem of soot related increases in lubricant viscosity by providing improved soot dispersion and toleration properties, particularly in diesel engines, and especially in heavy duty diesel engines employing exhaust gas recirculation.